1. Field of the Invention
The present invention relates to a welding material for use in hard-facing that portion of a cast iron base metal of a metallic press die (punch and/or matrix) or the like which needs to be increased in hardness, as well as to a method of determining the components of the welding material.
2. Description of Related Art
As a method of manufacturing a metallic trimming press die which is used in cutting a blank of a predetermined length from a metallic thin roll material of aluminum plate, steel plate or the like, or manufacturing a metallic trimming press die which is used in cutting unnecessary peripheral portion after having formed the blank by drawing in a metallic drawing die, there has hitherto been known a method of overlaying or cladding a welding material, which serves as a cutter material, onto that raw material for the metallic die which has been cast into a predetermined shape, and then cutting a cutter out of the overlaid or clad portion.
This kind of welding material for overlaying should preferably have a lower hardness after overlaying because the cutter must be cut into a predetermined shape by machining work. Once the cutter has been cut by machining work, however, it should preferably attain a high hardness relatively easily. There is known in Japanese Published Unexamined Patent Application No. 15481/1994 (corresponding to U.S. Pat. No. 5,361,968) a welding material in which a starting temperature of martensitic transformation (hereinafter called Ms temperature) of the welding material is set at 150.degree. C. or below, and the overlaid portion after overlaying has a hardness of HRC (Rockwell C Hardness) 45 or below and the hardness becomes HRC 45 or above by subjecting it, after welding, to a supercooling treatment at a temperature of 0.degree. C. or below.
The component composition (i.e., the composition of components) of the above-described conventional welding material is determined by using only the Ms temperature as a parameter. If the Ms temperature is lowered, a large amount of austenite is retained at room temperature and machining consequently becomes easy. It is, however, not clear by the Ms temperature alone whether the overlaid portion hardens up to a predetermined hardness after the supercooling treatment. Therefore, a large number of samples are conventionally prepared to determine the composition by actually carrying out the overlaying and the supercooling treatment, resulting in much time and expenses in determining the composition.
As a result of diligent studies and efforts, the inventors of the present invention have found out that there is a close relationship between each region in Schaeffler's structure diagram and the difference in hardness before and after the supercooling treatment. In other words, Schaeffler's structure diagram is a diagram which has a nickel (Ni) equivalent and a chromium (Cr) equivalent as parameters. It has thus been found out that a line of equal difference in hardness on which the difference in hardness before and after the supercooling treatment becomes equal (hereinafter called an "isohardness" line) can be drawn in the structure diagram.
Based on the above findings, the present invention has an object of providing a welding material which is easy in machining after welding and which can attain a sufficient hardness after the supercooling treatment, as well as a method of determining the components of the welding material.